In the early 1970's, several investigators demonstrated the existence of two .alpha.-Galactosidase isozymes designated A and B, which hydrolyzed the .alpha.-galactosidic linkages in 4-MU- and/or .rho.-NP-.alpha.-D-galactopyranosides (Kint, 1971, Arch. Int. Physiol. Biochem. 79:633-644; Beutler & Kuhl, 1972, Amer. J. Hum. Genet. 24:237-249; Romeo, et al., 1972, FEBS Lett. 27:161-166; Wood & Nadler, 1972, Am. J. Hum. Genet. 24:250-255; Ho, et al., 1972, Am. J. Hum. Genet. 24:256-266; Desnick, et al., 1973, J. Lab. Clin. Med. 81:157-171; and Desnick, et al., 1989, in The Metabolic Basis of Inherited Disease, Scriver, C. R., Beaudet, A. L. Sly, W. S. and Valle, D., eds, pp. 1751-1796, McGraw Hill, New York). In tissues, about 80%-90% of total .alpha.-Galactosidase (.alpha.-Gal) activity was due to a thermolabile, myoinositol-inhibitable .alpha.-Gal A isozyme, while a relatively thermostable, .alpha.-Gal B, accounted for the remainder. The two "isozymes" were separable by electrophoresis, isoelectric focusing, and ion exchange chromatography. After neuraminidase treatment, the electrophoretic migrations and pI value of .alpha.-Gal A and B were similar (Kint, 1971; Arch. Int. Physiol. Biochem. 79:633-644), initially suggesting that the two enzymes were the differentially glycosylated products of the same gene. The finding that the purified glycoprotein enzymes had similar physical properties including subunit molecular weight (-46 kDa), homodimeric structures, and amino acid compositions also indicated their structural relatedness (Beutler & Kuhl, 1972, J. Biol. Chem. 247:7195-7200; Callahan, et al., 1973, Biochem. Med. 7:424-431; Dean, et al., 1977, Biochem. Biophys. Res. Comm. 77:1411-1417; Schram, et al., 1977, Biochim. Biophys. Acta. 482:138-144; Kusiak, et al., 1978, J. Biol. Chem. 253:184-190; Dean, et al., 1979, J. Biol. Chem. 254:10001-10005; and Bishop, et al., 1980, in Enzyme Therapy in Genetic Disease:2, Desnick, R. J., ed., pp. 17-32, Alan R. Liss, Inc., New York). However, the subsequent demonstration that polyclonal antibodies against .alpha.-Gal A or B did not cross-react with the other enzyme (Beutler & Kuhl, 1972, J. Biol. Chem. 247:7195-7200; and Schram, et al., 1977, Biochim. Biophys. Acta. 482:138-144), that only .alpha.-Gal A activity was deficient in hemizygotes with Fabry disease (Kint, 1971, Arch. Int. Physiol. Biochem. 79:633-644; Beutler & Kuhl, 1972, Amer. J. Hum. Genet. 24:237-249; Romeo, et al., 1972, FEBS Lett. 27:161-166; Wood & Nadler, 1972, Am. J. Hum. Genet. 24:250-255; Ho, et al., 1972, Am. J. Hum. Genet. 24:256-266; Desnick, et al., 1973, J. Lab. Clin. Med. 81:157-171; Desnick, et al., 1989, in The Metabolic Basis of Inherited Disease, Scriver, C. R., Beaudet, A. L. Sly, W. S. and Valle, D., eds, pp. 1751-1796, McGraw Hill, New York; and, Beutler & Kuhl, 1972, J. Biol. Chem. 247:7195-7200); and that the genes for .alpha.-Gal A and B mapped to different chromosomes (Desnick, et al., 1989, in The Metabolic Basis of Inherited Disease, Scriver, C. R., Beaudet, A. L. Sly, W. S. and Valle, D., eds, pp. 1751-1796, McGraw Hill, New York; deGroot, et al., 1978, Hum. Genet. 44:305-312), clearly demonstrated that these enzymes were genetically distinct.